Demonstration of prion-like properties of mutant huntingtin fibrils in both in vitro and in vivo paradigms

Abstract

In recent years, evidence has accumulated to suggest that mutant huntingtin protein (mHTT) can spread into healthy tissue in a prion-like fashion. This theory, however, remains controversial. To fully address this concept and to understand the possible consequences of mHTT spreading to Huntington’s disease pathology, we investigated the effects of exogenous human fibrillar mHTT (Q48) and huntingtin (HTT) (Q25) N-terminal fragments in three cellular models and three distinct animal paradigms. For in vitro experiments, human neuronal cells [induced pluripotent stem cell-derived GABA neurons (iGABA) and (SH-SY5Y)] as well as human THP1-derived macrophages, were incubated with recombinant mHTT fibrils. Recombinant mHTT and HTT fibrils were taken up by all cell types, inducing cell morphology changes and death. Variations in HTT aggregation were further observed following incubation with fibrils in both THP1 and SH-SY5Y cells. For in vivo experiments, adult wild-type (WT) mice received a unilateral intracerebral cortical injection and R6/2 and WT pups were administered fibrils via bilateral intraventricular injections. In both protocols, the injection of Q48 fibrils resulted in cognitive deficits and increased anxiety-like behavior. Post-mortem analysis of adult WT mice indicated that most fibrils had been degraded/cleared from the brain by 14 months post-surgery. Despite the absence of fibrils at these later time points, a change in the staining pattern of endogenous HTT was detected. A similar change was revealed in post-mortem analysis of the R6/2 mice. These effects were specific to central administration of fibrils, as mice receiving intravenous injections were not characterized by behavioral changes. In fact, peripheral administration resulted in an immune response mounting against the fibrils. Together, the in vitro and in vivo data indicate that exogenously administered mHTT is capable of both causing and exacerbating disease pathology. Electronic supplementary material The online version of this article (10.1007/s00401-019-01973-6) contains supplementary material, which is available to authorized users.

Promiscuous Roles of Autophagy and Proteasome in Neurodegenerative Proteinopathies

“…This is supported by evidence that, similar to the prion protein and its misfolded scrapie isoform, undigested, misfold-prone proteins such as α-syn, tau, Aβ, huntingtin, SOD-1, TDP-43 and FUS can form intracellular aggregates in a self-templating manner [37][38][39][40][41][42][43][44]. In fact, these proteins possess prion-like properties, which allow spontaneous conversion of the normal isoform into abnormal ones spreading via cell-to-cell transmission [36][37][38][39][40][41][42][43][44][45][46].…”

Phagocytic glia are obligatory intermediates in transmission of mutant huntingtin aggregates across neuronal synapses

“…By contrast, wtHtt proteins containing polyQ≤36 tracts only aggregate upon nucleation by pre-formed Htt aggregate “seeds” (Chen et al, 2001; Preisinger et al, 1999). A growing body of evidence from cell culture (Chen et al, 2001; Costanzo et al, 2013; Holmes et al, 2013; Ren et al, 2009; Sharma and Subramaniam, 2019; Trevino et al, 2012) and in vivo (Ast et al, 2018; Babcock and Ganetzky, 2015; Jeon et al, 2016; Masnata et al, 2019; Pearce et al, 2015; Pecho-Vrieseling et al, 2014) models of HD supports the idea that pathogenic mHtt aggregates have prion-like properties— they transfer from cell to cell and template the conformational change of soluble wtHtt proteins. Here, we report that mHtt aggregates formed in presynaptic olfactory receptor neuron (ORN) axons effect prion-like conversion of wtHtt proteins expressed in the cytoplasm of their postsynaptic partner projection neurons (PNs) in the adult fly olfactory system.…”

The pathobiology of perturbed mutant huntingtin protein–protein interactions in Huntington's disease

“…In addition, the disease relevance of fibrillar mutant HTTex1 aggregates is supported by cell‐based assays indicating that such structures are rapidly taken up into cells (Ren et al ; Holmes et al ), possibly inducing toxicity. Furthermore, there is accumulating evidence that HTTex1 fibrils can self‐propagate and efficiently spread from cell to cell (Costanzo et al ; Babcock and Ganetzky ; Jeon et al ; Masnata et al ), suggesting that the active uptake and release of mHTT fibrils are important elements of pathogenesis and disease progression. The discovery that mutant HTTex1 seeding activity in fly neurons correlates with neurotoxicity and reduced survival supports this view (Ast et al ).…”